1. Field of the Invention
The present invention relates to a storage subsystem, and more particularly to remote copying of a storage subsystem for acquiring a write I/O log and a method of restoring a log during a disaster.
2. Description of the Prior Arts
A computer system has become commercially practical in which a computer and a storage system are connected together through a network, and data to be processed by the computer is transmitted and received via the network and is stored in the storage system. In online processing and batch processing that are to be carried out by the computer system, there may enter a situation in which these processing abnormally terminates by program bugs, failure of the storage system and the like to cause contradictions in the data stored in the storage system. Also, the data stored in the storage system may be erased by an artificial mistake.
In order to recover data of the computer system which has entered such a state, there is known a data recovery technique by way of backup and restoration of data as one of techniques for resuming processing suspended halfway by getting rid of the data contradiction, or doing over the processing suspended halfway again.
As conventional technique concerning the backup and restoration, in, for example, U.S. Pat. No. 5,263,154 (Patent Reference 1), there has been disclosed a technique in which data stored in the storage system at a point of time designated by the user is reproduced (hereinafter, referred to as “backup of data”) on a magnetic tape without stopping input and output (hereinafter, referred to as “I/O”) of data from a host connected to the storage system, and through the use of the data thus reproduced (hereinafter, referred to as “backup data”), the data is recovered (hereinafter, referred to as “restore”).
Also, in Japanese Published Unexamined Patent Application No. 2001-216185 (Patent Reference 2), in order to shorten time required to restore the data, there has been disclosed a technique in which information in a place where the data has been updated is retained as difference information after backup of the data is carried out, and when data stored in the storage system is restored with the backup data, only a portion of the backup data shown by the difference information is used to restore the data.
Also, in U.S. Pat. No. 5,544,347 (Patent Reference 3) and U.S. Pat. No. 5,742,792 (Patent Reference 4), there has been disclosed a technique for copying data by a remote storage system independently of the host. According to this technique, it is possible to make a copy of a business volume within the storage system which has been made by the host at a certain business site on a volume within the storage system at a remote site. For that reason, in consideration of a case where the business site suffers from a natural disaster and terrorism, the computer system causes an failure and the business cannot be continued, it is possible to prepare data for restoring the business at a remote site.